1. Field of the Invention
The present invention relates to a lap nipping mechanism in a comber which produces a thin sheet composed of fibers, so-called "fleece", by removing short fibers from a group of fibers, so-called "lap", in the manufacturing process of cotton yarn. In particular, the present invention relates to control of the rocking operation of a nipper frame in the lap nipping mechanism, the nipper frame having a cushion plate for use in nipping a lap.
2. Description of the Related Art
The average length of cotton fiber depends on its kind or its place of origin. Additionally, even in the same kind of cotton, its average fiber length is not constant and often varies. To produce high-grade cotton yarn with superior tenacity and appearance, it is necessary to remove short cotton fibers (including foreign matter such as nep). Use of a comber is an effective way to attain this objective.
Generally, a comber comprises a combing cylinder, a top comb, a pair of detaching rollers, and a nipper apparatus. The nipper apparatus rocks back and forth while nipping sheet-like fibers, so-called "lap", supplied thereto. The combing cylinder has a series of needles (i.e., cylinder needles) embedded on its peripheral surface (i.e., cylinder half lap). As the nipper apparatus moves backward (away from the detaching rollers), the needles comb the forward end of the lap. This action is called "combing". This combing action removes short fibers from the lap, producing a thin sheet-like fiber product, so-called "fleece".
The fleece is transferred forward as the nipper apparatus moves forward (towards the detaching rollers). As the newly combed fleece moves forward, the detaching rollers rotate in reverse and cause a preceding fleece, previously combed, to move rearward. As a result, the rear end of the preceding fleece is overlapped with the front end of a newly combed fleece (i.e., succeeding fleece). Then, the detaching rollers rotate in the forward direction of rotation, to pull out forward the pieced together fleeces. This action is called "piecing". During piecing process, the top comb combs the rear end of the succeeding fleece. In the combing process, these operations are repeated to effectively remove the short cotton fibers from the lap.
In general, the nipper apparatus comprises a nipper frame, a cushion plate fixed on the nipper frame at its front end, and a nipper knife to nip the lap in cooperation with the cushion plate. The nipper knife nips the lap at the tip of the cushion plate. The nipper frame can rock between a backmost position where the tip of the cushion plate is proximate to the cylinder needles and a foremost position where the tip is proximate to the detaching rollers.
Methods of rocking the nipper frame in a comber are roughly classified into the following three types according to a path drawn by the tip of the cushion plate.
(Type 1): A nipper frame is rockably supported by a rocking mechanism located above it. The tip of the cushion plate moves along a downward projecting arc, which is part of a circle adjacent to a circle drawn by the tips of cylinder needles when the combing cylinder runs. The circle drawn by the tips of the cylinder needles is hereinafter referred to as "cylinder circle".
(Type 2): A nipper frame is driven by a nipper shaft located below the frame, and is supported in a rockable manner by a four-node link mechanism with the nipper shaft as a stationary point in the link. As the nipper frame rocks, the tip of the cushion plate moves along an upward projecting arc, which is part of a circle encompassing the cylinder circle.
(Type 3): A nipper frame is designed so that the tip of the cushion plate moves along a substantially straight horizontal line, which is a path tangent to the cylinder circle.
In a type 1 apparatus, when the cushion plate moves, a section in which its tip approaches the cylinder circle is short. This results in insufficient combing. In a type 2 apparatus, the section in which the tip of the cushion plate approaches the cylinder circle is longer in comparison with the type 1 apparatus. This results in good combing. However, when the tip of the cushion plate reaches the foremost position in the rocking stroke, the tip is located below a position where a pair of upper and lower detaching rollers nip a succeeding fleece. Consequently, the front end of the succeeding fleece is likely to bend during piecing process. This may prevent smooth piecing. In addition, the rocking stroke of the nipper frame in the type 2 apparatus is greater than that in the type 1 apparatus, and hence the type 2 apparatus tends to generate vibrations during high-speed machine operation.
The type 3 apparatus is a compromise between the type 1 and 2 apparatuses. This design, however, caused insufficient combing and piecing operations. According to the type 3 design, the tip of the cushion plate approaches the cylinder needles at a position just over the cylinder circle. This increases the rocking stroke of the nipper frame.
In order to solve these problems, Japanese Unexamined Patent Publication No. 54-6926 discloses a method for controlling the rocking of the nipper frame as described below. In a total path along which the tip of the cushion plate together with the nipper frame rocks, there exists a point where the cushion plate tip nips a lap in cooperation with the nipper knife and releases the lap. The nip/release point is hereinafter referred to as "nipper opening/closing position". Its total path is divided into two sections: a front section between the foremost position and the nipper opening/closing position; and a rear section between the nipper opening/closing position and the backmost position.
In the rear section, the cushion plate tip moves along an upward projecting arc path in proximity to the cylinder circle. In the front section, the cushion plate tip moves upward along an inclined path coupled to the front end of the arc path in the rear section.
Specifically, a nipper frame 32 is rocked by a four-node link mechanism comprising a rocking lever 31, the nipper frame 32 and a following lever 33, as shown in FIGS. 5 and 6. During the rocking motion, a pivot 34 of the following lever 33, connected to the front portion of the nipper frame 32 is displaced. The following lever 33 is in a two-link structure comprising a first link 35 and a second link 36. The second link 36, forming the base portion of the following lever 33, is pressed against a stopper 38 by the action of a spring 37. When the tip of a cushion plate 40 is disposed in the front section, the first link 35 forming the distal end portion of the following lever 33 is able to pivot about a pivot 36a, while the first link 35 is integrated with the second link 36.
As shown in FIG. 5, when the tip of the cushion plate 40 is disposed in the rear section, the second link 36 does not pivot, but the first link 35 rocks about a pivot 35a. This rocking motion causes the tip of the cushion plate 40 to move along an upward projecting arc in proximity to a cylinder circle 41 as defined above.
As shown in FIG. 6, when the tip of the cushion plate 40 is disposed in the front section, the first and second links 35 and 36 pivot together as a unit about the pivot 36a. This pivoting motion causes the tip of the cushion plate 40 to move upward along an inclined path connecting the front point of the upward projecting arc path and a "nip position" where detaching rollers 39 nip a succeeding fleece therebetween. In this conventional method, however, the second link 36 supporting the nipper frame 32 repeatedly comes in contact with and moves away from the stopper 38, as the nipper frame 32 rocks. This repetitive action causes the second link 36 and the stopper 38 to wear off and generates noise and vibration. The noise and vibrations become more remarkable as the machine runs at higher speeds. Also, when lint is caught between the second link and the stopper, the nipper frame 32 cannot rock along the predetermined path.
According to a method of controlling nipper frame rocking disclosed in Japanese Unexamined Patent Publication No. 54-11335, when the cushion plate tip is disposed in the rear section, the cushion plate tip reciprocates along a path similar to the path disclosed in Japanese Unexamined Patent Publication No. 54-6926, as the nipper frame rocks. The cushion plate tip performs its cyclic motion along a predetermined path in the front section, so that the cushion plate tip goes upward along an inclined path toward the foremost position from the nipper opening/closing position, turns to the horizontal or downward direction to approach the nip position, and then returns downward along an inclined path to the nipper opening/closing position.
Specifically, as shown in FIGS. 7 and 8, a nipper apparatus used in this method comprises a four-node link mechanism made up of a rocking lever 31, a nipper frame 32, a following lever 43, and a rocking arm 44. The following lever 43 has a first end (upper end) linked to the nipper frame 32 at its forward portion, and a second end (lower end) linked to the rocking arm 44. The rocking arm 44 rocks up and down through a cam 46 fixed on a cylinder shaft 45. As the rocking arm 44 rocks, a pivot 43a is displaced up and down, and the tip of the cushion plate 40 rocks along the aforementioned predetermined path.
This nipper apparatus, however, not only requires lubrication for maintenance but also has a disadvantage in that lint is apt to be caught between the cam 46 and a cam roller 47 of the rocking arm 44. If lint is caught, the nipper frame 32 is prevented from rocking along a predetermined path. Also, using the cam 46 requires troublesome adjustments and its screws tend to loosen.